This invention pertains to the art of fluid control devices and more particularly to sealing means for such devices.
The invention is particularly applicable to a secondary seal arrangement for fluid control devices which control fluid flow from beverage dispensers, coffee urns and the like and will be described with particular reference thereto. However, it will be readily appreciated by those skilled in the art that the invention has broader application and has utility in many other environments.
Fluid control devices or faucets to which the subject invention is particularly directed utilize a stem member which is selectively reciprocable to move a valving member into and out of engagement with a sealing seat area for purposes of controlling fluid flow. In such devices, a primary stem packing or seal arrangement is employed for preventing undesired fluid flow outwardly of the device around the stem. Such stem packing or seals have taken many and varied forms and configurations in an effort to prevent such leakage. However, and regardless of these forms and design characteristics, the stem packings or seals eventually become ineffective or fail entirely due to the wearing effect of repetitive reciprocations of the stem in controlling fluid flow. When stem packing or seal failure occurs, fluid passing through the fluid control device or faucet is permitted to seep by or by-pass the stem seal resulting in valve leakage. When this situation occurs, it is necessary to disassemble the control device in order to replace the seal. In the event that the fluid control device is not continuously monitored, stem seal leakage can cause significant direct losses in system fluids, cause unnecessary housekeeping problems and possibly cause damage to equipment, materials and the like. The problem of stem seal wear and leakage generally increases as the pressure of the fluid being controlled increases.
To alleviate these problems, there have been some prior attempts to provide secondary stem seals or packings which would assume the necessary and appropriate stem sealing function in the event of primary stem seal failure. However, these attempts have not proved particularly successful because of the basic design concepts utilized. More particularly, prior secondary or backup seals have employed design characteristics substantially similar to the primary seals so that they were, in effect, continuously operative along with the primary seals. Thus, as the primary seals were worn due to continuous operative contact with the associated stems, the secondary or backup seals were similarly worn. Accordingly, when the primary seals failed and the secondary or backup seals were required to perform the stem sealing function, the secondary seals themselves had reached or were reaching the point of failure, having been subjected essentially to the same wear as the primary seals. In fact, in some prior secondary or backup seal designs, the secondary seals failed prior to failure of the primary seals.
For these reasons, it has been desired to develop a secondary or backup stem seal or packing arrangement which would not be subjected to significant wear until system fluid by-passed the primary seal or packing. This type of arrangement or system would then preserve the secondary or backup seal effectiveness for use only when and as necessary.
The present invention contemplates a new and improved structural arrangement which overcomes the foregoing problems and others and which provides a secondary seal or packing arrangement which is simple in design, economical to employ, performs a stem sealing function only when and as needed in response to a breakdown of the primary sealing arrangement and which is readily adapted for use in a number of different fluid control devices and environments.